Chromebook 11, cursor disappears

I'm seeing the same problem as others with my fleet of Chromebook 11s - students come in with no cursor on the screen and can only work with the keyboard. Rebooting often fixes it, but not always. Connecting a mouse works well, but we don't want to use them. It seems to be happening with the older machines, 2.5 years in service. 

It's a sporadic issue, but I've reproduced it with no extensions (logged in as Guest), and after powerwashing the devices. The one thing I can do to eliminate the problem is move the student to a Samsung or ASUS Chromebook - the problem goes away for good.

Any ideas what could be causing the issue with the 11 model?